In computing systems, such as desktop computers, portable computers, personal digital assistants (PDAs), servers, and others, storage devices are used to store data and program instructions. One type of storage device is a disk-based device, such as a magnetic disk drive (e.g., a floppy disk drive or hard disk drive) and an optical disk drive (e.g., a CD or DVD drive). Disk-based storage devices have a rotating storage medium with a relatively large storage capacity. However, disk-based storage devices offer relatively slow read-write speeds when compared to operating speeds of other components of a computing system, such as microprocessors and other semiconductor devices.
Another type of storage device is a solid state memory device, such as a dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, and electrically erasable and programmable read-only memory (EEPROM). Although solid state memory devices offer relatively high read-write speeds, usually on the order of nanoseconds, they have relatively limited storage capacities.
With improvements in nanotechnology (technology involving microscopic moving parts), other types of storage devices are being developed. One such storage device is based on atomic force microscopy (AFM), in which one or more microscopic scanning probes are used to read and write to a storage medium. Typically, a scanning probe has a tip that is contacted to a surface of the storage medium. Storage of data in the storage medium is based on perturbations created by the tip of the probe in the surface of the storage medium. In one implementation, a perturbation is a dent in the storage medium surface, with a dent representing a logical “1,” and the lack of a dent representing a logical “0.”
To perform a write operation, the probe of a probe-based storage device is heated to some predetermined temperature. Heating of the probe causes the tip of the probe to heat up to a write temperature that is high enough to soften the surface of the storage medium, thus imprinting a dent in the storage medium. However, it usually takes some amount of time to heat up the probe tip to the desired write temperature. During the initial stages of a write operation after some period of inactivity, the temperature of the probe tip may not be at the optimal write temperature. As a result, writing of the first few bits of data on a storage medium after some period of inactivity may be performed at a temperature that is less than the optimal level. Temperature variations of the probe tip can also occur between regions of the storage medium with a high density of dents and regions with a low density of dents. When writing to a region with a high density of dents, the probe tip is usually hotter than when the probe is writing to a region with a low density of dents.
Such variations in the temperature of the probe tip can lead to variations in the quality of dents formed in the storage medium. In areas of the storage medium where writing occurs at a temperature less than the optimal write temperature, appropriately sized dents may not be formed because the probe may not be hot enough to deform a desired amount of the storage medium. The improperly formed dents can be difficult to detect accurately during read operations. As a result, read errors may occur.